Method for reducing emission of pollutants from an internal combustion engine, and fuel emulsion comprising water and a liquid hydrocarbon

ABSTRACT

A fuel emulsion has a liquid hydrocarbon fuel, water, at least one emulsifier and at least one oxygen-containing water soluble organic compound. In the fuel emulsion, water is present in an amount not greater than 15% by weight, and the emulsifier is selected from a product obtained by reacting (a1) a polyolefin oligomer functionalized with at least one group deriving from a dicarboxylic acid, or a derivative thereof, with (a2) a polyoxyalkylene comprising linear oxyalkylene units. In the fuel emulsion, the oxygen-containing water soluble organic compound is present in a predetermined amount so as to obtain an amount of water soluble organic oxygen of from 0.1 to 5% by weight. A considerable reduction of particulate emissions is obtained by using this fuel emulsion while maintaining or even further reducing the NOx level which is already reduced by the engine itself.

The present invention relates to a method for reducing emission ofpollutants from an internal combustion engine, particularly from adiesel engine, and to a fuel emulsion comprising water and a liquidhydrocarbon.

It is known that the combustion of liquid hydrocarbons in an internalcombustion engine (e.g. a diesel engine) leads to the formation ofnumerous pollutants, in particular soot, particulates, carbon monoxide(CO), nitrogen oxides (NOx), sulphur oxides (SOx), and non-combustedhydrocarbons (HC), which cause a remarkable atmospheric pollution.

It is also known that the addition of controlled amounts of water to afuel can significantly reduce the production of pollutants. It isbelieved that this effect is the result of various phenomena arisingfrom the presence of water in the combustion zone. For example, thelowering of the peak combustion temperature by water reduces theemission of nitrogen oxides (NOx), the formation of which is promoted byhigh temperatures. In addition, the instantaneous vaporization of thewater droplets promotes better dispersion of the fuel in the combustionchamber, thereby significantly reducing the formation of soot,particulates and CO. These phenomena take place without adverselyaffecting the yield for the combustion process.

Several solution have been proposed to add water to liquid fuel at thetime of use, i.e. just before the fuel is injected into the combustionchamber, or directly into the chamber itself. However, these solutionsrequire modifications to be made to the structure of the engine and arenot capable of achieving optimum dispersion of the water in the fuel,which is an essential requisite for obtaining a significant reduction inpollutants without compromising the calorific yield for the process.

Thus, the most promising and numerous efforts made hitherto weredirected towards the formulation of emulsions between liquidhydrocarbons and water in the presence of emulsifiers (surfactants) forthe purpose of uniformly dispersing the water in the hydrocarbon phasein the form of droplets of the smallest possible size.

For example, European Patent Application EP-A-475,620 describesmicroemulsions of a diesel fuel with water, which contain a cetaneimprover and an emulsifying system comprising a hydrophilic surfactantand a lipophilic surfactant. These surfactants are selected fromethoxylated C₁₂-C₁₈ alkylammonium salts of a C₉-C₂₄ carboxylic orsulphonic acid: the hydrophilic surfactant contains at least sixethylene oxide units, while the lipophilic surfactant contains less thansix ethylene oxide units.

European Patent Application EP-A-630,398 describes a fuel in the form ofan emulsion consisting of a hydrocarbon fuel, from 3 to 35% by weight ofwater and at least 0.1% by weight of an emulsifying system consisting ofa sorbitan oleate, a polyalkylene glycol and an ethoxylated alkylphenol.

International Patent Application WO 97/34969 describes an emulsionbetween water and a hydrocarbon, for example a diesel fuel. Thisemulsion is stabilized by adding an emulsifier consisting of a sorbitansesquioleate, a polyethylene glycol monooleate and an ethoxylatednonylphenol. This emulsifier has an overall HLB (hydrophilic-lipophilicbalance) value of from 6 to 8.

A process for producing a stabilized emulsion of a liquid fuel and wateris described in European patent Application EP-A-812,615. This processinvolves preparing a first emulsion by mixing the fuel, the water and asurfactant, and subsequently mixing the emulsion thus obtained with morewater to give the final emulsion. The emulsion is stabilized using ahydrophilic surfactant or a lipophilic surfactant, or a mixture thereof.Lipophilic surfactants which can be used are fatty acid esters ofsorbitol, for example sorbitan monooleate, while hydrophilic surfactantswhich are suitable for this purpose are fatty acid esters of sorbitolcontaining a polyp alkylene chain, for example polyoxyethylene sorbitantrioleate. Further stabilization of the emulsion can be obtained byadding ethylene glycol or a polyethylene glycol.

International Patent Application WO 92/19701 describes a process forreducing the emission of NOx from a gas turbine, in which an emulsion ofwater with a diesel fuel is used. The emulsion is stabilized by addingan emulsifier selected from alkanelamides obtained by condensing analkylamine or hydroxyalkylamine with a fatty acid; and ethoxylatedalkylphenols. The emulsifier preferably has a HLB value of less than orequal to 8. Physical stabilizers such as waxes, cellulose derivatives orresins can be added to improve the stability. As described in patentapplication WO 93/07238, the above emulsion can be further stabilized byadding a difunctional block polymer with a primary hydroxyl end group,in particular containing propylene a copolymer oxide/ethylene oxideblocks.

International Patent Application WO 00/15740 describes an emulsifiedwater-blended fuel composition comprising: (A) a hydrocarbon boiling inthe gasoline or diesel range; (B) water; (C) a minor emulsifying amountof at least one fuel-soluble salt made by reacting (C) (I) at least oneacylating agent having about 16 to 500 carbon atoms with (C) (II)ammonia and/or at least one amine; and (D) about 0.001 to about 15% byweight of the water-blended fuel composition of a water soluble,ashless, halogen-, boron-, and phosphorus-free, amine salt, distinctfrom component (C). The acylating agent (C) (I) includes carboxylicacids and their reactive equivalents such acid halides, anhydrides, andesters, including partial esters and triglycerides. The fuel may alsocomprise other components such as cosurfactants selected from ionic ornon-ionic compounds having a HLB of from 2 to 10, preferably of from 4to 8; organic cetane improvers, including nitrate esters of substitutedor unsubstituted aliphatic or cycloaliphatic alcohols; antifreezeagents, usually an alcohol such as ethylene glycol, propylene glycol,methanol, ethanol, and mixtures thereof, in an amount of from 0.1% to10%, preferably from 0.1 to 5%, by weight of the fuel composition.

International Patent Application WO 01/51593 describes a fuel comprisingan emulsion between water and a liquid hydrocarbon, and furthercomprising as emulsifier a polymeric surfactant obtainable by reactionbetween: (i) a polyolefin oligomer functionalized with at least onegroup deriving from a dicarboxylic acid, or a derivative thereof; and(ii) a polyoxyalkylene comprising linear oxyalkylene units, saidpolyoxyalkylene being linked to a long-chain alkyl group optionallycontaining one or more ethylenic unsaturations. The fuel may alsocomprise an alcohol as antifreeze agent, such as methanol, ethanol,isopropanol, or a glycol, in an amount generally from 0.5 to 8% byweight, preferably from 1 to 4% by weight, with respect to the totalweight of the fuel.

A reduction of NOx exhaust emissions from a diesel engine can also beobtained by controlling the functioning of the engine so as to obtain areduction of the peak combustion temperature.

Such a reduction may be obtained for instance by recirculation of aportion of the exhaust gases into the engine intake manifold where itmixes with the incoming air/fuel charge. By diluting the air/fuelmixture under these conditions, peak combustion temperatures arereduced, resulting in an overall reduction of NOx output. Such systemsare commonly known as Exhaust Gas Recirculation (EGR) systems. The firstEGR systems were introduced in the early '70s as on/off devices.However, continuous recirculation of the exhaust gases resulted inunstable engine operation, decreased power output and oil contaminationdue to the presence of particulates in the recirculated gases. Uponintroduction of close loop computer controls for engines, the EGRsystems were remarkably improved by controlling the rate or amount ofrecirculated exhaust gases in a manner responsive to operatingconditions of the engine, particularly during acceleration. For ageneral review on EGR systems see for instance “Emission Controls: PartII: GM Exhaust Gas Recirculation Systems” by M. Schultz, published inMotor, Vol. 159 (February 1883), pages 15 ff, and also U.S. Pat. No.3,796,049 and No. 4,454,854.

Another system for reducing the peak combustion temperature, and thusthe NOx emissions, by controlling the functioning of the engine is basedon an electronic control of the injection timing in the combustionchamber. Particularly, delayed injection reduces NOx emissions, whileexcessive delay results in higher fuel consumption and HC emissions.Therefore, a precise injection timing is necessary, which is guaranteedby an electronic diesel-control system (EDC). A crankshaft referencepoint provides the basis for regulating the timing device setting.Extremely high precision can be achieved by monitoring the start ofinjection directly at the injection nozzle by employing a needle-motionsensor to monitor the needle-valve movement (control of start ofinjection) (see for instance U.S. Pat. No 5,445,128).

Another known method to reduce NOx in exhaust gases is based on coolingcompressed intake air in turbocharged engines, so as to reducecombustion temperatures in the engine, with a consequent decrease of NOxemissions. A method of this kind is disclosed for instance in U.S. Pat.No. 6,145,498.

For a general review on engine measures to reduce exhaust emissions fromdiesel engines see for instance “Bosch Automotive Handbook”, 4thEdition, October 1996 (pages 530-535)

In order to meet the requirements of increasingly more stringentemission standards, some attempts have been made to combine differenttechnologies of emission reduction.

For instance, in U.S. Pat. No. 4,479,473 a system for controllingemissions from a diesel engine is disclosed by controlling therecirculation of engine exhaust gases into the intake manifold and bymodulating the injection timing schedule of the engine fuel in pump.

U.S. Pat. No. 5,271,370 discloses an emulsion fuel engine having atleast one cylinder with an injection nozzle for injecting an emulsionfuel, which has been formed by mixing a first fuel with a second fuel,into the cylinder. The engine comprises exhaust gas recirculation meansfor returning a portion of exhaust gas to an intake passage torecirculate the exhaust gas; and exhaust gas recirculation control meansfor controlling the amount of the exhaust gas to be recirculated.Therefore, water and diesel fuel are mixed for the first time when theengine is operated by the emulsion fuel. Alternatively, an emulsion fuelprepared in advance by mixing diesel fuel and water and stored in anemulsion fuel tank can be delivered to the injection nozzle and theninjected into the cylinder.

The Applicant has felt the need of combining techniques for controllingthe peak combustion temperature such as those described above with theuse of a fuel emulsion which can be fed to the combustion chamberwithout introducing further modifications to the engine.

Moreover, the Applicant has perceived the importance of providing a fuelemulsion containing a reduced amount of water without decreasing thecapability of the fuel emulsion to reduce pollutants emission,particularly particulate emission.

The Applicant has now found that the above goal and other remarkableimprovements may be achieved by fueling an internal combustion enginewhose functioning is controlled so as to obtain a reduction of the peakcombustion temperature with a fuel emulsion comprising a liquidhydrocarbon fuels water, at least one emulsifier and at least oneoxygen-containing water soluble organic compound. The use of this fuelemulsion allows to obtain a considerable reduction of particulateemissions while maintaining or even further reducing the NOx level whichis already reduced by the engine itself. A reduced amount of water inthe fuel emulsion is of great importance, since it allows not tosubstantially affect the power output of the engine, thus allowing theuse of the fuel emulsion also in applications where the power loss is aconstraint, such as heavy load trucks and passenger cars. Moreover, inthe case of EGR systems, a low level of particulate emission allows toreduce oil contamination.

Therefore, in a first aspect the present invention relates to a methodfor reducing emission of pollutants from an internal combustion engineincluding at least one combustion chamber, comprising injecting a fuelemulsion into the at least one combustion chamber;

-   igniting the fuel emulsion in the at least one combustion chamber in    the presence of air;-   operating the internal combustion engine so as to reduce peak    combustion temperature in the at least one combustion chamber;-   wherein the fuel emulsion comprises a liquid hydrocarbon fuel,    water, at least one emulsifier and at least one oxygen-containing    water soluble organic compound.

According to a preferred embodiment, operating the internal combustionengine so as to reduce peak combustion temperature in the at least onecombustion chamber comprises recirculating a portion of exhaust gasesproduced during ignition into the at least one combustion chamber.

According to another preferred embodiment, operating the internalcombustion engine so as to reduce peak combustion temperature in the atleast one combustion chamber comprises controlling injection timing ofthe fuel emulsion in the combustion chamber.

According to another preferred embodiment, operating the internalcombustion engine so as to reduce peak combustion temperature in the atleast one combustion chamber comprises compressing and cooling intakeair before entering the combustion chamber.

According to a preferred embodiment, in the method according to thepresent invention the amount of water in the fuel emulsion is notgreater than 15% by weight, preferably from 2 to 12% by weight, morepreferably from 2.5 to 10% by weight, even more preferably from 3 to 8%by weight.

According to another preferred embodiment, in the method according tothe present invention the amount of oxygen-containing water solubleorganic compound is predetermined so as to obtain an amount of watersoluble organic oxygen of from 0.1 to 5% by weight, preferably from 0.3to 4% by weight, more preferably from 0.5 to 2.5% by weight, even morepreferably from 0.8 to 2% by weight.

Unless otherwise specified, in the present description and claims theamounts are expressed as % by weight with respect to the total weight ofthe fuel emulsion.

In another aspect, the present invention relates to a fuel emulsioncomprising a liquid hydrocarbon fuel, water, at least one emulsifier andat least one oxygen-containing water soluble organic compound asadditive for reducing emission of pollutants, especially of particulate,wherein the amount of water in the fuel emulsion is not greater than 15%by weight, preferably from 2 to 12% by weight, more preferably from 2.5to 10% by weight, even more preferably from 3 to 8% by weight, and theamount of oxygen-containing water soluble organic compound ispredetermined so as to obtain an amount of water soluble organic oxygenof from 0.1 to 5% by weight, preferably from 0.3 to 4% by weight, morepreferably from 0.5 to 2.5% by weight, even more preferably from 0.8 to2% by weight.

In another aspect, the present invention relates to a method forreducing emission of pollutants, especially of particulate, from aninternal combustion engine fuelled by a fuel emulsion comprising ahydrocarbon phase and an aqueous phase dispersed in the hydrocarbonphase, the method comprising adding to the fuel emulsion at least oneoxygen-containing water soluble organic compound so as to obtain apredetermined amount of water soluble organic oxygen in the aqueousphase.

In another aspect, the present invention relates to the use of anoxygen-containing water soluble organic compound to reduce emission ofpollutants, particularly of particulate, from an internal combustionengine fuelled by a fuel emulsion.

The Applicant wishes to point out that the fuel emulsions according tothe present invention are particularly suitable for use in fueldistribution networks dedicated to fuelling of heavy load trucks and/orpassenger cars, where the need of a fuel which is able to reducepollutant emissions, especially particulate, without substantiallyaffecting the power output of the engine is requested.

Therefore, according to another aspect, the present invention relates tothe use a fuel emulsion comprising a liquid hydrocarbon fuel, water, atleast one emulsifier and at least one oxygen-containing water solubleorganic compound as fuel in a distribution network for fuelling heavyload trucks and/or passenger cars.

The amount of water soluble organic oxygen is the amount of oxygenlinked to the oxygen-containing water soluble organic compound dissolvedin the aqueous phase of the fuel emulsion. It can be determined on thebasis of the number of oxygen atoms contained in the water solublecompound, assuming that the overall amount of that compound added to thefuel emulsion is dissolved in the aqueous phase.

The water soluble compound according to the present invention (for thesake of conciseness identified herein also as “water soluble compound”)is a non-ionic organic compound having at least one oxygen-containinggroup, soluble in water at 20° C., usually not containing otherheteroatoms such as sulfur, nitrogen, phosphorus, halogens. Preferablythe oxygen-containing group may be selected from hydroxyl group, ethergroup, ester group, ketone group, peroxy group, and combinationsthereof.

Preferably, the water soluble compound has a solubility in water at 20°C. of at least 5% by weight, more preferably of at least 8% by weight.

The oxygen-containing water soluble organic compound according to thepresent invention may be selected from:

(i) alcohols, such as methanol, ethanol, 1 propanol, 2-propanol,1-butanol, 2-butanol, 2-methyl 1-propanol, diacetone alcohol, furfurylalcohol;

(ii) glycols such as ethylene glycol, diethylene glycol, triethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, butanediol,1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,3-hexanediol,1,3-propanediol, 2,3-hexandiol, polyethylene glycol;

(iii) polyols such as glycerol, diglycerol, sorbitol, glycerol2-methylether, glycerol trimethylether, glycerol monoacetate, fructose,galactose, sucrose, pentaerythritol, dipentaerythritol,tripentaerythritol;

(iv) esters such as: ethyl acetate, methyl acetate, butyl acetate, ethylacetoacetate, ethylene glycol acetate, ethylene glycol diacetate, methyllactate, ethyl lactate, glycerolmonoacetate, isopropyllactate,methylformate, ethylformate, butylformate, isopropylformate;

(v) ethers, such as: ethylene glycol diethylether, ethylene glycolmonoethylether, ethylene glycol glycol monoisopropylether, ethylenemonobutylether, diethylene glycol dimethylether, diethylene glycolmonoethylether, ethylene glycol dimethylether, ethylene glycolmonobutylether, triethylene glycol monoethylether, triethylene glycoldimethylether, tetraethylene glycol dimethylether, polyethylene glycoldimethylether;

(vi) ketones, such as: 2-propanone, 2-pentanone, 3-nentanone,2-methyl-3-pentanone, 3-hydroxy-2-pentanone, 4-hydroxy-2-pentanone,5-hydroxy-2-pentanone; or mixtures thereof.

The fuel emulsions according to the present invention comprises at leastone emulsifier The emulsifier, or the combination of emulsifiers, has ahydrophilic-lipophilic balance (HLB) of from 2 to 10, preferably from 3to 8.

The emulsifier is generally soluble in the hydrocarbon fuel and may beselected from one of the following classes of products:

(a) a product obtained by reacting (a1) a polyolefin oligomerfunctionalized with at least one group deriving from a dicarboxylicacid, or a derivative thereof, with (a2) a polyoxyalkylene comprisinglinear oxyalkylene units, said polyoxyalkylene being linked to along-chain alkyl group optionally containing one or more ethylenicunsaturation;

(b) a product obtained by reacting (b1) a hydrocarbyl substitutedcarboxylic acid acylating agent with (b2) ammonia or an amine, thehydrocarbyl substituent of said acylating agent having from 50 to 500carbon atoms.

Other emulsifiers my be selected from: alkanolamides,alkylarylsulfonates, amine oxides, poly(oxyalkylene)compounds (includingethyleneoxide propyleneoxide block copolymers), carboxylated alcoholethoxylates, ethoxylated alcohols, ethoxylated alkyl phenols,ethoxylated amines and amides, ethoxylated fatty acids, ethoxylatedfatty esters and oils, fatty esters, glycerol esters, glycol esters,imidazoline derivatives, lecithin and derivatives, lignin andderivatives, monoglycerides and derivatives, olefin sulfonates,phosphate esters and derivatives, propoxylated and ethoxylated fattyacids or alcohols or alkylphenols, sorbitan derivatives, sucrose estersand derivatives, sulfates or alcohols or ethoxylated alcohols or fattyesters, and mixtures thereof.

More details on emulsifiers that can be used in the present inventioncan be found in EP-A-475,620, EP-A-630,398, WO 97/34969, EP-A-812,615,WO 92/19701, WO 93/07238, WO 00/15740 and WO 01/51593, which are hereinincorporated by reference.

The amount of the at least one emulsifier to be used in the fuelemulsion according to the present invention is predetermined mainly as afunction of the amount of water to be emulsified and of the type ofliquid hydrocarbon fuel. Preferably, the at least one emulsifier is usedin an amount of from 0.1 to 10% by weight, preferably from 0.5 to 5% byweight.

The fuel emulsion according to the present invention is generally of thewater-in-oil type, wherein the water droplets are dispersed in thecontinuous hydrocarbon phase.

The fuel according to the present invention includes a liquidhydrocarbon fuel, generally deriving from the distillation of petroleumand consisting essentially of mixtures of aliphatic, naphthenic,olefinic and/or aromatic hydrocarbons. The liquid hydrocarbon generallyhas a viscosity at 40° C. of from 1 to 53 cSt, and a density at 15° C.of from 0.75 to 1.1 kg/dm³, and can be selected, for example, from gasoils for use as automotive fuels or for production of heats fuel oils,kerosenes, aviation fuels (Jet Fuels).

The water to be used in the fuel emulsion can be of any type, forexample industrial or domestic mains water. However, it is preferred touse demineralized or deionised water, in order to avoid the formation ofmineral deposits on the internal surface of the combustion chamberand/or on the injectors.

The fuel emulsion according to the present invention may contain otheradditives, such asp cetane improvers, corrosion inhibitors, lubricants,biocides, antifoaming agents, and mixtures thereof.

In particular, the cetane improvers are products which improve thedetonating properties of the fuel, and are generally selected fromnitrates, nitrites and peroxides of the organic or inorganic type, whichare soluble in the aqueous phase or, preferably, soluble in thehydrocarbon phase, such as organic nitrates (see for example patentsEP-475,620 and U.S. Pat. No. 5,669,938). Of preferred use are alkyl orcycloalkyl nitrates containing up to 10 carbon atoms, such as: ethylnitrate, amyl nitrates, n-hexyl nitrate, 2-ethylhexyl nitrate, n-decylnitrate, cyclohexyl nitrate and the like, or mixtures thereof.

The biocides can be selected from those known in the art, such asmorpholine derivatives, isothiazolin-3-one derivatives,tris(hydroxymethyl)nitromethane, formaldehyde, oxazolidines, bronopol(2-bromo-24nitro-1,3-propandiol), 2-phenoxyethanol, dimethylolurea, ormixtures thereof.

The oxygen-containing water soluble organic compound which is added tothe fuel emulsion according to the present invention may act also asantifreeze. However, for some applications it could be advisable to addto the fuel emulsion also an antifreeze selected from those available inthe art.

The fuel emulsions according to the present invention may also includeat least one water soluble amine or ammonia salt, such as ammoniumnitrate, ammonium acetate, methyalmmonium nitrate, methylammoniumacetate, ethylene diamine diacetate, urea nitrate, urea dinitrate, ormixtures thereof, in an amount of from 0.001% to 15% by weight (see WO00/15740).

The fuel emulsion according to the present invention is generallyprepared by mixing the components using an emulsifying device, in whichthe formation of the emulsion can result from a mechanical-type actionexerted by moving parts, or from passing the components to be emulsifiedinto mixing devices of static type, or alternatively from a combinedmechanical and static action. The emulsion is formed by feeding theaqueous phase and the hydrocarbon phase, optionally premixed, into theemulsifying device. The emulsifier and the other additives which may bepresent can be introduced separately or, preferably, premixed either inthe aqueous phase or in the hydrocarbon phase depending on theirsolubility properties. Preferably, the oxygen-containing water solubleorganic compound is premixed in the aqueous phase, while the emulsifieris premixed in the hydrocarbon phase.

The present invention will now be further illustrated by means of someworking examples.

The fuels having the compositions reported in Table 1 were tested on adiesel engine used on cars Volkswagen Passat 1.9 TDI 130 cv, having anEGR system and a fuel injection unit pump, The engine was tested on achassis rolls dynamometer according to the European standard ECER15+EUDC. The measurement cycle reproduced a urban driving cycle (ECE)combined with an extra-urban driving (EUDC) segment to account for moreaggressive, high speed driving modes. The emissions were measuredaccording to that standard and expressed as grams of pollutant per km ofroute.

The results are reported in Table 2.

TABLE 1 FUEL 1 2 3 4 5 Diesel Fuel 100 86.22  90.22  87.22 92.22 EN590Water — 12.00  8.00  8.00  4.00 Emulsifier — 1.60 1.60  1.60  1 60 MEG —— —  3.00 (*)  2.00 (**) Cetane — 0.15 0.15  0.15  0.15 ImproverBactericide — 0.03 0.03  0.03  0.03 The compositions are expressed as %by weight. Emulsifier: obtained by reacting a polyoxyethylene-fatty acidmonoester with a polyisobutene functionalized with maleic anhydride(according to Example 1 of WO 01/51593); MEG: monoethyleneglycol; Cetaneimprover: 2-ethylhexyl nitrate; Bactericide: isothiazolin-3-onederivative. (*) corresponding to 1.55% by weight of water solubleorganic oxygen; (**) corresponding to 1.03% by weight of water solubleorganic oxygen.

TABLE 2 FUEL 1 2 3 4 5 NOx 0.448 0.404 0.345 0.375 0.362 (g/km)Particulate 0.035 0.020 0.020 0.010 0.013 (g/km) CO 0.276 0.422 0.3560.400 0.201 (g/km)

1-38. (canceled)
 39. A fuel emulsion comprising: a liquid hydrocarbonfuel, water, at least one emulsifier, and at least one oxygen-containingwater soluble organic compound as additive for reducing emission ofpollutants, wherein water is present in an amount not greater than 15%by weight, the at least one emulsifier is selected from a productobtained by reacting (a1) a polyolefin oligomer functionalized with atleast one group deriving from a dicarboxylic acid, or a derivativethereof, with (a2) a polyoxyalkylene comprising linear oxyalkyleneunits, said polyoxyalkylene being linked to a long-chain alkyl groupoptionally containing one or more ethylenic unsaturation, the at leastone oxygen-containing water soluble organic compound is present in apredetermined amount so as to obtain an amount of water soluble organicoxygen of from 0.1 to 5% by weight, and the at least oneoxygen-containing water soluble organic compound is selected from mono-,di-, and tri-alkylene glycols, and mixtures thereof.
 40. The fuelemulsion according to claim 39, wherein the water is present in anamount of 2 to 12% by weight.
 41. The fuel emulsion according to claim40, wherein the water is present in an amount of 2.5 to 10% by weight.42. The fuel emulsion according to claim 41, wherein the water ispresent in an amount of 3 to 8% by weight.
 43. The fuel emulsionaccording to claim 39, wherein the oxygen-containing water solubleorganic compound is present in a predetermined amount so as to obtain anamount of water soluble organic oxygen of 0.3 to 5% by weight.
 44. Thefuel emulsion according to claim 43, wherein the oxygen-containing watersoluble organic compound is present in a predetermined amount so as toobtain an amount of water soluble organic oxygen of 0.5 to 2.5% byweight.
 45. The fuel emulsion according to claim 44, wherein theoxygen-containing water soluble organic compound is present in apredetermined amount so as to obtain an amount of water soluble organicoxygen of 0.8 to 2% by weight.
 46. The fuel emulsion according to claim39, wherein the oxygen-containing water soluble organic compound has asolubility in water at 20° C. of at least 5% by weight.
 47. The fuelemulsion according to claim 46, wherein the oxygen-containing watersoluble organic compound has a solubility in water at 20° C. of at least8% by weight.
 48. The fuel emulsion according to claim 39, wherein theemulsifier has a hydrophilic-lipophilic balance (HLB) of 2 to
 10. 49.The fuel emulsion according to claim 48, wherein the emulsifier has ahydrophilic-lipophilic balance (HLB) of 3 to
 8. 50. The fuel emulsionaccording to claim 39, wherein the emulsifier is present in an amount of0.1 to 10% by weight.
 51. The fuel emulsion according to claim 50,wherein the emulsifier is present in an amount of 0.5 to 5% by weight.